Trump has endorsed McCain, though earlier this campaign cycle he disregarded the 80-year-old senator's status as a war hero

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In this file photo, U.S. Sen. John McCain, R-Ariz., speaks at Phoenix Firehouse 30 after receiving an endorsement from the Professional Firefighters of Arizona, on Monday, Aug. 29, 2016.

Incumbent U.S. Sen. John McCain is running for re-nomination in Arizona's primary election Tuesday, and he is expected to defeat his leading opponent, former state senator Kelli Ward. For her part, Ward has adopted a Trump-like style of rhetoric during her campaign, highlighting the scourge of illegal immigration and opposing amnesty measures for the undocumented, NBC News reported.

Trump has endorsed McCain, though earlier this campaign cycle he disregarded the 80-year-old senator's status as a war hero. McCain has also agreed to support Trump's presidential run, even though he came out against the real estate mogul's statements about the parents of a fallen soldier who spoke against Trump at the GOP convention.

An unexpected loss for McCain in the primary would indicate a rising backlash against establishment GOP politicians. McCain is also predicted to defeat the favorite potential Democratic nominee, Ann Kirkpatrick, in a general election, though the Democratic contender is expected to use McCain's endorsement of Trump against him.